must darken
Regular verb: darken - darkened- darkened

Affirmation 	
Simple form 	V-ing form 	Perfect 	V-ing perfect 	
I must darken
you must darken
he must darken
we must darken
you must darken
they must darken 	I must be darkening
you must be darkening
he must be darkening
we must be darkening
you must be darkening
they must be darkening	I must have darkened
you must have darkened
he must have darkened
we must have darkened
you must have darkened
they must have darkened	I must have been darkening
you must have been darkening
he must have been darkening
we must have been darkening
you must have been darkening
they must have been darkening	

Negation 	
Simple form 	V-ing form 	Perfect 	V-ing perfect 	
I mustn't darken
you mustn't darken
he mustn't darken
we mustn't darken
you mustn't darken
they mustn't darken 	I mustn't be darkening
you mustn't be darkening
he mustn't be darkening
we mustn't be darkening
you mustn't be darkening
they mustn't be darkening	I mustn't have darkened
you mustn't have darkened
he mustn't have darkened
we mustn't have darkened
you mustn't have darkened
they mustn't have darkened	I mustn't have been darkening
you mustn't have been darkening
he mustn't have been darkening
we mustn't have been darkening
you mustn't have been darkening
they mustn't have been darkening	

Interrogative form 	
Simple form 	V-ing form 	Perfect 	V-ing perfect 	
must I darken?
must you darken?
must he darken?
must we darken?
must you darken?
must they darken? 	must I be darkening?
must you be darkening?
must he be darkening?
must we be darkening?
must you be darkening?
must they be darkening? 	must I have darkened?
must you have darkened?
must he have darkened?
must we have darkened?
must you have darkened?
must they have darkened? 	must I have been darkening?
must you have been darkening?
must he have been darkening?
must we have been darkening?
must you have been darkening?
must they have been darkening? 	

Interro-negative form 	
Simple form 	V-ing form 	Perfect 	V-ing perfect 	
mustn't I darken?
mustn't you darken?
mustn't he darken?
mustn't we darken?
mustn't you darken?
mustn't they darken? 	mustn't I be darkening?
mustn't you be darkening?
mustn't he be darkening?
mustn't we be darkening?
mustn't you be darkening?
mustn't they be darkening? 	mustn't I have darkened?
mustn't you have darkened?
mustn't he have darkened?
mustn't we have darkened?
mustn't you have darkened?
mustn't they have darkened? 	mustn't I have been darkening?
mustn't you have been darkening?
mustn't he have been darkening?
mustn't we have been darkening?
mustn't you have been darkening?
mustn't they have been darkening?